1. Field of the Invention
The present invention relates to a packing system including a preformed packing for packing the stuffing-box of valves used for controlling the flow of fluids.
2. Description of the Related Art
Valves used for controlling the flow of fluids typically have a valve stem that passes into the body of the valve or valve housing. The stem is linked to a gate or other movable member located within the valve housing. The gate seats against valve seats provided in the valve housing to shut off the flow of fluid. Fluid flows through the valve when the gate is moved away from its seats by the action of the valve stem. At this time fluid can leak out of the valve through the opening which allows the stem to pass into the valve housing. Typically a stuffing box is provided around the opening for the valve stem. This stuffing box is packed with packing material, typically a stack of packing rings. A gland follower or a gland nut is then used to crush the packing down in the stuffing-box to provide a positive seal around the valve stem.
The conventional method of preventing leakage around the valve stem suffers from a number of drawbacks. Foremost among these drawbacks is that the old method of replacing the packing is time consuming and tedious, requiring the loosening of the gland fasteners, removing the yoke, removing the gland follower, removing the old packing using packing picks and pullers, and using a flashlight and mirror to check the stuffing-box for cleanliness. Also, the valve must be disassembled to allow replacement of the packing rings around the valve stem.
To overcome the drawbacks enumerated above alternative methods and arrangements for valve packing have been proposed in the prior art.
U.S. Pat. No. 31,512, issued to John H. Gould on Feb. 19, 1861, shows a metal alloy packing for the stuffing box of the piston rod of a steam engine. The packing of Gould is in the form of a metal alloy cylinder having a flange at each end.
U.S. Pat. No. 458,453, issued to Addison Goodrich on Aug. 25, 1891, shows a packing extractor resembling a hollow nut which is inserted into a stuffing-box before the packing is inserted. The packing is actually contained in the extractor which allows easy removal of the packing.
U.S. Pat. No. 975,045, issued to Wills Johnson on Nov. 8, 1910, shows a removable stuffing box which uses conventional packing.
U.S. Pat. No. 1,052,726, issued to Charles W. G. King on Feb. 11, 1913, shows a packing material that incorporates a perforated metal sheet. The packing material of king is in the form of segments with tapered ends. When such segments are wrapped around a shaft, the tapered ends overlap to form a joint. Perforated metal sheets are used to reinforce the tapered ends and thus keep them from breaking.
U.S. Pat. No. 1,211,476, issued to Norman Bruce Miller on Jan. 9, 1917, shows a packing material that is in sheet form. Right triangular pieces of the sheet are glued along their hypotenuse and then rolled to form packing material.
U.S. Pat. No. 1,557,945, issued to Charles A. Schlotter et al. on Oct. 20, 1925, shows a packing ring that is diagonally split and has an inner perforated metal ring for support.
U.S. Pat. No. 1,798,268, issued to John Mellor on Mar. 31, 1931, shows a packing material composed of a compressible metal ring filled with a compressible lubricating material.
U.S. Pat. No. 2,050,620, issued to Frank N. Mason on Aug. 11, 1936, shows a packing ring composed of a compressible metal ring filled with a compressible packing material and having a pair of copper bearing rings along an inner circumference thereof.
U.S. Pat. No. 2,417,799, issued to Donald A. Seaver on Mar. 18, 1947, shows a gland nut for compressing packing material in a stuffing box.
U.S. Pat. No. 5,476,271, issued to Paul Hatting et al. on Dec. 19, 1995, shows a packing material in the form of a metal bellows.
U.S. Pat. No. 5,524,902, issued to Kevin R. Cornette on Jun. 11, 1996, shows a packing material having tapered ends which is adhesively attached to a gland nut. U.S. Pat. No. 5,524,902, which is incorporated herein by reference, lists a voluminous number of references relating to the art of sealing around movable shafts.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. In particular, none of the above inventions and patents describe a preformed packing having an inner cylindrical shell surrounded by an outer cylindrical shell with the inner cylindrical shell extending for some distance beyond both ends of the outer cylindrical shell.